Laminate structures which is composed of a plurality of thin films formed on a base member are employed in a variety of technical fields. For example, a thin film is formed on a base member made of an inorganic or organic material, thereby forming an electronic device or protecting a surface of the base member as a protective film.
In such a laminate structure, high adhesive strength of the thin film to the base member surface is often required so as to ensure reliability of the device, or for other reasons. Accordingly, in order to enhance the adhesion, various methods have been proposed, such as cleaning the base member surface or improving the surface quality, and providing an adhesion layer between the base member and the thin film.
Cleaning of the base member surface is commonly performed through a base member washing treatment employing an organic solvent, acid, or alkali, a UV ozone treatment, or a plasma treatment, as examples. These treatments are usually performed as the thin film is formed on a glass substrate or an inorganic material substrate such as an Si substrate, and some of the washing methods improve the surface state, as described in “Thin Film” by Sadafumi Yoshida (Baifukan, 1990).
With regard to improvement of surface quality of a base member, a method has been provided for partially carbonizing a color filter or an organic protective film which is formed covering the color film, so as to enhance adhesion between the color film and a transparent electrode made of an ITO (Indium Tin Oxide) film which are formed on a glass substrate provided on one side of a liquid crystal panel, for example. Japanese Patent Laid-Open Publication No. Hei 10-319226 describes, for example, formation of a carbonized layer between a color filter and a transparent electrode by exposing the color filter or an organic protective film formed on the color filter to DC-plasma or RF-plasma for a short period of time or applying, before an adhesion layer is formed, ion irradiation to the color filter or the organic protective film which have been formed. The above publication describes that with such a carbonized layer, the protective function of the base layer is improved and also adhesion of the base layer with respect to the adhesion layer and the transparent electrode, which are formed above the base layer, can be enhanced.
Formation of an adhesion layer between a base member and a thin film includes cases in which, for example, a hard coat layer is formed on a surface of plastic lens. Plastic lens is a soft material and must therefore to be covered with a hard coat layer for surface protection. However, because adhesion between the plastic lens and the hard coat material is low, in many cases, sufficient durability cannot be secured when a hard coat layer is formed directly on the lens surface. To address this problem, Japanese Patent Laid-Open Publication No. 2000-205305 proposes that a primer layer made of metal oxide particles dispersed in a resin is coated and dried on the plastic lens surface and then an adhesion layer is formed. It is reported that adhesion of a hard coat layer to the plastic lens can be enhanced by thus forming a primer layer on the plastic lens surface and then forming a hard coat layer thereon.
Further, in the field of a semiconductor devices or the like, it is required that a polymer resin having a relative dielectric constant lower than that of an inorganic film be used for an insulating film such as an inter-layer insulating film. However, sufficient adhesion cannot be secured between an insulating layer made of a polymer resin and metal lines. In order to deal with this problem, Japanese Patent Laid-Open Publication No. Hei 6-283615, for example, discloses that an adhesion layer made of an amorphous fluorocarbon polymer with many dangling bonds is interposed between an insulating layer made of the above-described polymer resin and a metal layer (including a metal line).
In addition, recently, there has been an increasing demand for a lighter and thinner electronic device which is formed on a plastic substrate used in place of a glass substrate. Because a plastic material cannot provide high shielding property against foreign impurities (such as water and oxygen) which an electronic device wishes to avoid, it is necessary to form a barrier layer between the substrate and the electronic device. However, adhesion between the plastic substrate and the barrier layer remains low and requires further improvement. In this regard, Japanese Patent Laid-Open Publication No. 2002-18994 proposes provision of an adhesion layer made of Si or the like between the plastic layer and the barrier layer, and reports that adhesion between the plastic substrate and the barrier layer is increased due to the provision of the adhesion layer.
Improvement in the state of a substrate surface can be recognized when a washing treatment using an organic solvent or acid and alkali, and an UV ozone treatment or a plasma treatment are employed with respect to a substrate surface. However, organic base members such as a plastic substrate and a film substrate are often eroded by chemicals such as an organic solvent, acid, and alkali, and therefore cannot be washed sufficiently to remove all foreign substances and contaminants from the surface. Further, however the surface of the base member is cleaned, such cleaning will not improve the inherent adhesiveness between materials having a low chemical bonding power.
According to the plasma treatment of organic base members such as a plastic substrate and a film substrate, although the nature of the surface can be modified, due to high plasma energy, a modified layer is formed through the layers to a region which is rather far from the surface, and therefore the original property of the substrate is often lost. Moreover, when a plasma treatment is performed using a mixture of discharge gas and oxidizing gas such as oxygen so as to increase cleanness of the substrate, ashing is performed through the layers to a deep portion far from the substrate surface, and also evenness of the substrate surface is lost.
With a primer layer as described in the above Japanese Patent Laid-Open Publication No. 2000-206305, formation of a uniform and precise thin film remains an industrially difficult task, and in many cases, the resulting film cannot maintain sufficient adhesive force under severe environment and is peeled off. Also, in optical element and light emissive element applications it is necessary that an adhesion layer be optically transparent, which is difficult with either a transparent metal thin film or a Si film.
In addition, with the use of amorphous fluorocarbon polymer having many dangling bonds as an adhesion layer, adhesion between an insulating layer made of a polymer resin and such an amorphous fluorocarbon polymer layer is enhanced, resulting in an increased adhesion strength between the insulating layer and a metal layer. However, because fluorocarbon polymer, even in an amorphous state, includes substantially no elements which form strong chemical bonding between layers, it cannot maintain a sufficient adhesion force in a more severe environment, with the result that metal layers are often peeled off.
As described above, none of the above-described conventional methods are sufficient to improve adhesion between layers. Further, with the variety of types of base members and thin film materials which are used today, there is a strong demand that high adhesion (a high level of adhesive strength) be provided with respect to a variety of materials and that adhesion between layers be maintained even in a severe environment.
Further, in a laminate structure in which one or more thin films made of an inorganic or organic material are formed on a base member made of an inorganic or organic material, a protective film which is formed so as to protect the laminated thin films from erosion by moisture, oxygen and corrosive gas existing in the air and from mixture of impurities or the like is required in a variety of technical fields. However, with the progress of diversification of base members and development of a device such as an organic electroluminescence element including a mixture of an inorganic material layer and an organic material layer, in addition to excellent shielding ability against foreign materials or high strength, further functions are required for these devices and the film itself which directly covers the base member for protection. For example, an ability to cover a device or a base member, as the object of protection, with high adhesion and stability for a long period whether or not the protection object is made of an organic material or an inorganic material, and an ability to prevent damage to the protection object and significant stress generated with respect to the protection object when forming the protective layer are required. However, while protective films preferably providing one of the two abilities has been proposed, no protective layers having the combination of functions described above, especially those functions which require trade-off have yet been proposed.
In order to solve the above problems, the present invention has an advantage of realizing an adhesion layer, a protective layer, or the like, which can be applied to either an organic material or an inorganic material.